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1

8i6

.Appendix II.

ways  of cutting a screw-thread upon a spindle, which may be
thus enumerated:

(i.) Cutting with ,$•&£& 0»/ dies as described at p. 192. This
principle is defective, for reasons there mentioned. The cor-
responding socket is screwed with taps.

(2.) Screwing in the lathe, described at pp. 147, 212, and 484.
This is the only method giving a perfect screw, except that next
mentioned, and is really equivalent to scale copying.

(3.) Copying is generally performed in a turret-head lathe as at
p;2ooj hut is also shewn at 47, Fig. 317, p. 349, for screwing
.stay tubes, The copy is often of a larger scale than the work.

(4.) By Chasing only.    On p, 212 the chaser is described a&